The invention was developed in response to a need for centralized remote control and dimming of street lights in metropolitan areas, and it will be described in conjunction with that application which is well illustrative of its utility. City street lights are frequently energized in groups of up to 50 on 230 volt, 60 Hz A.C. power lines. One or more such lines radiate from local controller boxes, of which there may be from a few hundred up to several thousand scattered throughout the city, depending upon its size. Typically, each controller box was originally equipped with a main breaker, a clock timer and on-off switches controlled by the timer. The timer may require periodiq resetting to assure accord with the seasonal changes in the hours of daylight and darkness, and there is no provision for dimming.
It is desired to replace the local control of street lights by remote control under a master controller in the form of a programmable computer at the utilities control center of the city. The control signals are to be transmitted by standard telephone line to a centrally located frequency-modulated paging transmitter operating in the UHF band, for instance at about 450 MHz. The paging transmitter is used primarily for paging and for voice messages to city employees, but the channel is to be shared by interspersing the signals for lighting control among the other messages.
The plan calls for modifying the local controller boxes by removing the clock timers and equipping them with FM receivers tuned to the paging frequency. Upon reception of an appropriate signal by the receiver, the 230 v, 60 Hz power line from the controller box to the street luminaires is to be turned off or on according to the signal. Dimming of selected luminaires is to be achieved by sending to them an appropriate signal causing dimming means to be switched into circuit with the lamp.